FR3060865A1 - METHOD FOR PRODUCING AN ASSEMBLY OF GONIOMETRY ANTENNAS AND ANTENNA ASSEMBLY PRODUCED ACCORDING TO SUCH A METHOD - Google Patents

Abstract

The present invention relates to the field of interception of electromagnetic signals. It relates more particularly to a method of manufacturing a set of direction finding antennas in two dimensions comprising a step of designing said set of antennas from predetermined constraints, said design step comprising: - a step (21) of definition of a reference antenna array, - a step (22) of searching configurations to take into consideration each of the antennas forming a set of direction finding antennas, - A step (23) of quantization of the maximum level of ambiguities of each of the possible configurations from a correlation function in order to associate to each of the configurations considered an evaluation quantity, - a step (24) of searching and selecting the configuration presenting the evaluation quantity the weaker.

Description

Holder (s): THALES.

Extension request (s)

Agent (s): MARKS & CLERK FRANCE General partnership.

FR 3 060 865 - A1 (54) METHOD FOR PRODUCING AN ANTENNA ASSEMBLY PRODUCED ACCORDING TO SUCH A METHOD.

(© The present invention relates to the field of interception of electromagnetic signals. It relates more particularly to a method of manufacturing a set of direction finding antennas in two dimensions comprising a step of designing said set of antennas from constraints predetermined, said design step comprising:

- A step (21) of defining a network of reference antennas,

A step (22) of searching for configurations to be taken into consideration for each of the antennas forming a set of direction finding antennas,

A step (23) of quantifying the maximum level of ambiguity of each of the possible configurations from a correlation function in order to associate with each of the configurations considered an evaluation quantity,

- A step (24) of finding and selecting the configuration having the lowest evaluation quantity.

GONIOMETRY ANTENNAS AND ASSEMBLY

Method for producing a set of direction finding antennas and antenna assembly produced according to such a method

The subject of the present invention is a method for producing a set of direction finding antennas and an antenna assembly produced according to such a method. The invention is particularly applicable in the field of detection of radio signals in electronic warfare (Electronic Support in English), these signals being able to come from radars, telecommunication transmitters or any other device radiating such a signal.

The invention relates more particularly to direction finding and more precisely to a method of manufacturing a set of direction finding antennas capable of measuring the direction of arrival of a radio signal. The invention also relates to a set of direction finding antennas produced according to such a method.

Generally speaking, electronic warfare applications are concerned with very brief signals, this is particularly true for radar signals. This leads to realizations of goniometers necessarily leaning on a set of several fixed antennas which, illuminated by the radio signal of interest, will deliver a set of signals captured at the same time, this set carrying the direction of arrival (Direction O f Arraiai or DOA in English) of said signal. Several estimators exist to calculate the direction of arrival. Before calculating, one need is to acquire this set of signals, which involves as many reception chains as there are antennas. As reception chains are relatively expensive material entities, it is therefore important to optimize their number, that is to say to design sets of direction-finding antennas for which it is sought either to maximize the performance at a given number of antennas , or to minimize the number of antennas with given performances.

The design of a set of direction finding antennas must generally comply with specifications setting the requirements, which can be expressed in three categories:

- A first category concerns the characteristics of the antennas used to build the set of direction finding antennas. For each antenna, there is its gain (amplitude and phase) as a function of the direction of arrival, the frequency and the polarization of the incident radio signal.

- A second category concerns the geometric constraints, on the carrier platform, of placement of the set of direction finding antennas, including the relative positions of the antennas. These constraints describe at least the area covered by each antenna and the maximum area allocated to accommodate the set of direction finding antennas. In fact, there is a minimum spacing between antennas.

- A third category describes the performance to be achieved by the user device of the set of direction finding antennas. Among these, the spatial, frequency and polarization coverage, the accuracy and the rate of goniometry ambiguities.

Thereafter, we will speak of goniometry ambiguity. This problem exists when the set of direction finding antennas has two similar, or very similar, responses for two sufficiently different directions of arrival. This is due in principle to the fact that a phase shift is only measured to a whole number of times 2π near. So when two antennas are not less than half a wavelength from an incident signal, the geometric phase difference between the antenna's phase centers, which can exceed 2π, will be measured with ambiguity and the direction of arrival that the goniometer will provide will be ambiguous.

This problem is well known in interferometers. One solution then consists in using an irregular arrangement of the antennas to vary the angular spacing of the ambiguities from one pair of antennas to the other. A judicious arrangement of the antennas thus finally makes it possible to exploit the redundancy of the information measured by the different pairs of antennas to unambiguously determine the direction of arrival.

This well-known interferometry technique exploits only the phase shifts between antennas without taking account of the amplitude. Since the amplitude would make sense by the definition of the constituent antennas, it would be wise to use this amplitude to improve the direction of arrival measurements.

In addition, the sets of interferometric goniometry antennas, or interferometry bases, are very generally antennas aligned in the desired angular measurement plane. If the direction of arrival of the incident radio signal is in an inclined plane with respect to this measurement plane, then the measurement may be very wrong. This is why, we are obliged to compensate a site interferometer in site as soon as it has to work in a range of sites which is sufficiently large with regard to its precision in field; it is then necessary to add, for example, to a field interferometer, a site goniometer which can also be an interferometer. In such a case, all the antennas do not participate directly in the estimation of the two angles but indirectly by correction. This type of solution is therefore unsuitable for dimensioning a set of direction finding antennas in which all the antennas are used directly to jointly estimate the two angles. Furthermore, this technique is also difficult to develop for a set of direction finding antennas in which the antennas have different adapted polarizations, since the phase difference between two antennas is then no longer linked to the single direction. arrival, but also depends on the polarization of the incident radio signal.

An object of the invention is in particular to correct all or part of the drawbacks of the prior art by proposing a solution making it possible to estimate the direction of arrival of an incident signal according to two dimensions.

To this end, the subject of the invention is a method of manufacturing a set of direction-finding antennas in two dimensions comprising at least three antennas, comprising a phase of determining the optimal configuration of said set from a list of possible configurations, a configuration being defined by the gain, the pointing direction and the position within said set of each of said antennas, said phase comprises at least:

- A step of defining a network of reference antennas, said array covering a surface having a dimension in site and / or in deposit inversely proportional respectively to a level of precision required in site and / or in deposit for the estimation directions of arrival of the incident waves, and comprising a plurality of elementary antennas, said elementary antennas being distributed in a regular mesh, the distance separating two contiguous elementary antennas being substantially equal to the half-wavelength associated with the frequency maximum of a range of frequencies of interest,

- A step of searching for configurations to be taken into account based on predetermined constraints in order to establish a list of configurations to be taken into account,

- A step of quantifying the maximum level of ambiguity of each of the configurations of said list from a correlation function in order to associate with each of said configurations an evaluation quantity,

- A step of finding the configuration with the lowest evaluation quantity, said configuration being the optimal configuration.

In a particular embodiment, said set of direction-finding antennas being intended for measurements of direction of arrival of incident radio signals not depending on the polarization of these said signals, the evaluation quantity associated with a configuration is equal to the maximum value of a correlation function Fcor (Θ _{1 (} Θ ₂ ) function of two directions of arrival where Θ _χ and 0 ₂ representing two directions of arrival sweeping the area of coverage of direction of arrival of said configuration for one and the direction of arrival direction of interest for the other, and excluding the values for which the correlation function of said array of reference antennas F _CorRéf (0 _{1 (} 0 ₂ ) is greater than or equal to a predetermined threshold S _Re f, the correlation functions Fcor ^e t

FcorRéf (θι, Θ ₂ ) expressing themselves respectively from the pointing vector of said configuration and from the pointing vector of said reference set.

In another possible embodiment, said antenna assembly being intended for measurements of direction of arrival of incident radio signals depending on the polarization of these said signals, the evaluation quantity associated with a configuration is equal to the maximum value of the eigenvalues of a matrix Γ * (Θ _{1 (} Θ ₂ ) · Γ (Θ ₁ , Θ ₂ ), function of two directions of arrival where 0 _X and 0 ₂ representing two directions of arrival sweeping the area of angular coverage of said configuration for one and the angular domain of interest for the other, where:

^ HnormC ^ li ^ min)

Γ (Θ _η Θ ₂ ) = [^ Read,

Vnorm min (Θι, [UHnorm (.®2> ^ min) ^ Vnorm (. ^ 2i

OR

- Γ (0 _1; 0 ₂ ) is a 2x2 square matrix;

- m ⁿ ° ^rm S ¹ 'is a 2 x N matrix;

Î ^ Hnorm (^ 2> ^ min ^ ^ Vnorm (®2> ^ min)] © St A matrix N X 2,

- U _Hnorm (Q, A _min ) and U _Vnorm (Q, A _min ) are two vectors forming an orthonormal base of the plane generated by the two pointing vectors (/ ^ (0,2 ^) and U _v (Q, A _min ) of the set of goniometry antennas at the minimum wavelength, respectively in horizontal rectilinear polarization and in vertical rectilinear polarization,

- The sign * corresponds to the transposed and conjugated transformation.

The list of configurations to be taken into account corresponds for example to the complete list of possible configurations.

In another possible embodiment, the list of configurations to be taken into account corresponds for example to a random drawing of a predetermined number of configurations from the complete list of possible configurations.

The antennas of reference antenna arrays being aligned according to a mesh, the positions in the possible configurations of the antennas of the set of direction-finding antennas are for example aligned on said mesh.

Said array of reference antennas is for example an array of radiating elements, each antenna of said set of direction finding antennas being produced from a sub-array of said array.

The invention also relates to a set of direction finding antennas obtained by such a process.

Other particularities and advantages of the present invention will appear more clearly on reading the description below, given by way of nonlimiting illustration, and made with reference to the appended drawings for which:

- Figure 1 illustrates a definition of the geometric reference system used and particular angles of deposit and site;

- Figure 2 shows possible steps in the design of a set of direction-finding antennas in two dimensions;

- Figure 3 shows an exemplary embodiment of a set of direction-finding antennas according to two dimensions in the case of non-dependence on polarization;

- Figure 4 shows an exemplary embodiment of a set of direction-finding antennas according to two dimensions in the case of polarization dependence (case of polarization diversity);

- Figures 5a and 5b are graphical representations of the correlation functions of the set of direction finding antennas corresponding to the configuration shown in Figure 3 and of the reference antenna array, respectively Fcor (Θι, Θ ₂ ) and ^E CorRé / (®l <®2)!

- Figure 6 illustrates a definition of the geometric reference frame used with a set of polarization diversity direction finding antennas;

- Figure 7 is a graphic representation of the generalized correlation (matrix calculation) of the set of goniometry antennas with diversity of polarization materialized in Figure 6;

- Figures 8a and 8b respectively represent a configuration of a set of direction finding antennas designed according to the invention and the graph of the correlation function illustrating the results obtained for this configuration;

- Figures 9a and 9b respectively represent a configuration of a set of polarization diversity direction finding antennas designed according to the invention and the generalized correlation graph illustrating the results obtained for this configuration.

The present invention relates to a method for producing a set of direction finding antennas that can work according to two angular dimensions, for example deposit and site. If necessary, the method is obviously applicable with a single angular dimension.

Figure 1 recalls that, for any direction of arrival, materialized by a line of direction of arrival 11, the deposit is the angle formed by the line 110, corresponding to the projection of the line of direction of arrival on the horizontal plane, and a reference axis in this horizontal plane (or center line, for example normal to a plane of alignment of the antennas). The site is the angle formed by the arrival direction line 11 and its projection 110 on the horizontal plane.

In the following, we will use the term direction of arrival, symbolized by Θ, and therefore generally defined by two angles, the deposit θ ₃ and the site 0 _S , Θ = (θ ₃ , θ ₅ ).

The set of goniometry antennas can be produced both from conventional non-network antennas (spiral, sinuous, butterfly, cornet, etc.) as from a network antenna in which we define a set of sub-arrays, this set forming said set of direction finding antennas. In other words, the assembly is then produced from beams formed with sub-arrays of a network of elementary antennas.

The method according to the invention comprises a phase of searching for the optimal configuration of the set of direction finding antennas followed by a phase of making from this optimal configuration.

Generally, by configuration, we understand the definition of each constitutive antenna within the assembly, that is to say the gain as a function of the direction of arrival, of the frequency and of the polarization, the position of the phase center and the direction of pointing, whatever the embodiment with conventional antennas or with formed beams. This exhaustive definition of a configuration can however be simplified as will be seen below.

The method according to the invention comprises for example the following steps presented in FIG. 2:

- A first step 21 of defining a network of reference antennas;

- A second step 22 of defining the configurations to be taken into consideration;

- A third step 23 of evaluation of each configuration to be taken into consideration, by a method involving the network of reference antennas and making it possible to assess the quality of direction-finding in terms of ambiguities and precision;

- A fourth step 24 of determining the best configuration;

- A fifth step 25 of producing the set of direction finding antennas corresponding to this better configuration.

The first step in defining a reference antenna array consists in defining a plurality of K elementary antennas, all identical, the phase centers of which are regularly arranged on a mesh surface. The distance between two contiguous antennas of the array must be significantly less than the minimum half-wavelength, the minimum wavelength A _min corresponding to the maximum working frequency f _max , which is the maximum frequency of a range of frequencies of interest, specific to each application. The lengths of the network, in the horizontal and vertical cutting planes, are inversely proportional to the precision of direction-finding respectively in bearing and in elevation.

Generally, this mesh surface is not necessarily planar, it can for example be cylindrical. However, a simplified variant may be a planar mesh surface.

This array of reference antennas is a simple calculation device in the process in the case where the set of direction-finding antennas is produced with conventional antennas. On the other hand, in the case where the set of direction-finding antennas is produced by beams formed from sub-arrays, this array of reference antennas can correspond concretely to the array of elementary antennas with which the sub-arrays are made - networks generating said beams formed.

The purpose of the second step of defining the configurations to be taken into consideration is to provide the third step with a list of configurations to be evaluated so that the fourth step can choose, among them, the best one according to a criterion on the quantity used to evaluate each configuration.

Recall that a configuration corresponds to the physical definition of a set of goniometry antennas, this set comprising N antennas, N being an integer greater than or equal to 2. This physical definition corresponds, for each of the N constituent antennas in the most general case, gain depending on the direction of arrival, frequency and polarization, the position of the phase center and the pointing direction. This applies regardless of the embodiment, with conventional antennas or with formed beams.

Defining a configuration can however be simplified in a large number of possible cases. An alternative embodiment can then lead to a configuration which is reduced solely to the positions of the phase centers of the antennas in a plane, these being all identical, placed in a plane and pointed in the same direction.

Note that the antenna gain (depending on the direction of arrival, frequency and polarization) is a definition for generalization. Indeed, for common use cases, we will not tend to use constituent antennas different from each other, except in polarization response for reasons of polarization diversity.

These configurations are framed by the specifications and by geometric and technical considerations depending on the embodiment of the set of direction finding antennas. For example, in the case of an embodiment with conventional antennas, the antennas must neither obstruct mechanically nor hide, they will not be able to overlap. On the other hand, in the case of beams formed, the antennas could overlap to the extent that the beams formation by sub-network would allow it; it is a technical question of specifications.

The reference antenna array, defined in the first step, provides the regular mesh of the implantation surface of the phase centers of the K antennas constituting this array, with a mesh pitch d substantially less than half the length d minimum wave A _min / 2. The phase centers of the antennas constituting the set of goniometry antennas, forming beams, being able to align with a half-step of mesh d / 2 depending on the beam formation, this mesh can be used at half not also when the antennas are conventional.

FIG. 3 illustrates an exemplary plan of embodiment of a set of direction finding antennas 30 as well as the possible positions of each of the phase centers of the antennas thus produced with the subarrays 31. In order not to overload the figure, only the possible locations 311 of the phase centers 310 of each of the antennas 31 have been shown.

According to a first mode of implementation, during this step, one can constitute a list of all the possible configurations of the set of antennas of direction finding, by establishing all the possible combinations taking into account the constraints and the specifications. .

According to a second alternative mode of implementation, the list of configurations to be evaluated can be established by randomly selecting, from the set of possible configurations, a number of configurations restricted relative to the total possible. The purpose of this mode is to avoid too many configurations to be evaluated in the third step, if the application is constrained in runtime. Insofar as the configurations are limited to the positions of the phase centers of the antennas, it is interesting to note that a random drawing will reproduce the statistics of irregularity of the configurations, so that one may have, in the list thus restricted, a configuration sufficiently irregular to have a sufficiently low level of ambiguity in direction finding.

The third step is based on an evaluation of the maximum level of direction-finding ambiguities produced by each configuration of set of direction-finding antennas, each evaluated configuration having been defined in the second step.

Ambiguity in direction finding corresponds to identical arrival direction measurements for different actual arrival directions. In practice, given the imperfections in the production of equipment and measurement noises of all kinds, an ambiguity of goniometry corresponds to measurements of direction of arrival close to real directions of arrival sufficiently distant.

The level of goniometry ambiguities can be evaluated by the correlation of the directions of arrival directions carried out by a set of goniometry antennas in a given direction directions domain, by eliminating from this domain the cases for which the correlation direction of arrival measurements is normal, which can be seen in the correlation of the direction of arrival measurements of the reference antenna array which produces an ideal response.

Correlation can be supported by a more or less generalized correlation function calculation depending on whether the direction of arrival measurements depend or not on the polarization of the radio signals to be processed.

To perform this calculation, we need to distinguish two areas of arrival directions: the coverage area and the area of interest. The coverage area is the area of arrival directions for which the set of direction finding antennas can receive radio signals. The area of interest is given by the specifications, it is at most equal to the coverage area, it is generally restricted in relation to the latter.

In a practical way to calculate the more or less generalized correlation functions, one will be able to take angular values not linearly distributed in these fields, but angular values whose sines are linearly distributed. This advantageously makes it possible to reduce the number of arrival directions while taking into account, if necessary, the widening of the beams formed linked to the depointing.

The first case is that where the direction of arrival measurements made with the set of direction finding antennas do not depend on the polarization of the incident radio signals. In this case, the correlation is expressed by a simple correlation function. The maximum level of ambiguity of a set of direction finding antennas, associated with a given configuration, corresponds to the maximum value of the correlation function of said set max _{0l; 02} (F _Cor (0 _{1 (} 0 ₂ )) where 0! And 0 ₂ are two directions of arrival sweeping the coverage domain for one and the domain of interest for the other (the assignment of the domains to Θχ and to 0 ₂ is indifferent), and excluding the values for which the correlation function of the reference antenna array F _CorRef (B ₁ , Q ₂ ') is greater than or equal to a predetermined threshold S _Ref Generally, the result is between 0 and 1 bound A preferential value of the S _Ref threshold is 0.5.

The correlation functions F _Cor (Q ₁ , Q ₂ ) and F _CorRéf (Q _it Q ₂ ) are expressed respectively from the pointing vector (or steering vector in English) of the set of goniometry antennas U ( Q, A _min ) and of the pointing vector of the reference antenna array U _Re f (&, A _min ):

Fcor (®M = læ (0x, A _min ) U (0 ₂ , A _min ) l ² and

Fcoriïéf (®l> ®2) | ^ Ré / (®l '^ - min) ^ -m / n) | where the sign * corresponds to the transposed and conjugated transformation.

Generally, a pointing vector of a group G of P antennas, i / _c (0, A), is a unit vector comprising P components, the p-th component of which is proportional to the response of the p -th

27Γ j antenna, in amplitude and phase, A _Cp (Q, A) = D _Gp (Q, A) e ^J T ' ^0Mc p' ^u ^ _o ù as illustrated in Figure 1:

- D _Gp (Q, X) is the radiation or gain diagram (amplitude and phase) of the p-th antenna of group G in the direction of arrival 0 and at the wavelength A;

- M _Gp is the position in space of the phase center of the p-th antenna of group G with respect to an origin O;

- u (0) is the unit vector carried by the direction of arrival 0;

- _re p _r ESENTE the term phase shift related to the position of the phase of the p-th antenna center in the group G.

In general, the pointing vector l / _G (0, Â) can be expressed as the ratio of the vector Α _α (Θ, λ), whose p-th component is 4 _β , ρ (Θ, Λ ), to its Euclidean norm IM _G (0, Λ) || which itself can be expressed in the following way IM _G (0, Â) || = JA _G (Q, A) -yl _G (0, Â), A _G (Q, A) is the conjugate transposed vector of the vector A _G (0.2).

The pointing vector U (Q, A _min ) is obtained by applying the above to the N antennas of the set of goniometry antennas.

The pointing vector U _Ref (Q, At _min ) is obtained by applying the above to the K antennas of the reference antenna array. Generally taking into account the weak directivity of the antennas of the reference antenna array, in an implementation variant, the gains D _Refk (Q, X) can be replaced by 1. In another implementation variant, these gains can be replaced by weighting coefficients P _k different from one antenna to another, in order not to penalize a configuration of the set of direction finding antennas offering a lower level of ambiguity at the cost of one slight deterioration in the direction of arrival precision.

The second case is that where the arrival direction measurements made with the set of direction finding antennas depend on the polarization of the radio signals, both for reasons of polarization diversity of the incident radio signals and for reasons of response in polarization of the constituent antennas. When the set of direction finding antennas must be able to process a diversity of polarization of incident signals, constituent antennas must be used which can form a basis for decomposition of the polarization, which is preferably orthogonal. For example, conventionally used antennas of horizontal rectilinear adapted polarization and antennas of vertical rectilinear adapted polarization are conventionally used. But it can also be antennas of right circular adapted polarization and antennas of left circular adapted polarization.

In this case, the correlation at the level of the set of goniometry antennas is assessed with the matrix product Γ * (Θ _{1 (} Θ ₂ ) · Γ (Θ _{1 (} Θ ₂ ) and the maximum level of ambiguities corresponds to the greatest eigenvalue of this matrix product:

 with max

Γ (Θ _η Θ ₂ ) =

or :

max means maximum eigenvalue; Γ (Θι, θ ₂ ) is a 2x2 square matrix;

[^ Hnorm (θΐ "1min) Uvnormfàl’ 1min) is a 2 x N matrix;

Î ^ Hnorm (®2 »1min) Uvnorm (®2> lmin) l ®St A matrix N X 2,

- UHnorm (®> lmm) ^{and u} vnorm (. ^Q , l _m in) are two vectors forming an orthonormal base of the plane generated by the two pointing vectors U _H (Q, l _min ) and U _v (Q, l _min ) of the set of antennas of goniometry at the minimum wavelength, respectively in horizontal rectilinear polarization (H) (corresponding to an electric field collinear with the vector u _H (0) of 'Figure 4, said vector being a unit vector orthogonal to the right of direction of arrival defined by Θ and located in the local horizontal plane of the set of goniometry antennas) and in vertical rectilinear polarization (V) (corresponding to a collinear electric field with the vector u _v (Q) of FIG. 4, said vector being a unit vector orthogonal to the line of direction of arrival defined by Θ and located in the local vertical plane, including the line of direction of arrival, of the set d 'goniometry antennas), which can take, for example, the following form :

U,

Vnorm (Q,! _M i _n ) -

UHnormfà> 1min) ~ U H (® ’1min)

Uv (Q, l _m in) ~ (Ph (®> 1min) 'Uv (®>1min))' Uh (®> 1min)

11 ^ 1 / (0.2 ^) - (UÎ {(Q, l _min ) l / _v (&, A _min )) υ _Η (Θ, λ „

- The sign * corresponds to the transposed and conjugated transformation.

The pointing vectors U _H (@, At _min ) and U _v (Q, A _min ) are unit vectors comprising N components because they correspond to the set of antennae with goniometry which has N antennas, their nth components are proportional to the responses, in amplitude and phase, of the n-th antennas respectively in horizontal polarization ^ H, n (Fl, l) = D _Hn (Q, A) e ^j T ' ^0Mn ' ^u ^ and in vertical polarization Α _νη (Θ, λ) = _{ϋ νη} (Θ, λ) _e JT ' ^0Mn ' ^{u (e} \ where similarly to the first case and as illustrated by figure 4:

- ΰ _Ηη (β, λ) and ΰ _νη (Θ, λ) are the radiation or gain diagrams (amplitude and phase) of the n-th antenna of the set of goniometry antennas in the direction of arrival Θ , at the wavelength λ and respectively in horizontal rectilinear polarization and in vertical rectilinear polarization;

- M _n is the position in space of the phase center of the n-th antenna of the set of goniometry antennas with respect to an origin O;

- u (0) is the unit vector carried by the direction of arrival Θ;

- _e 7y; -OM "-u (0) _re p _r e t _{e sen} | _e phase shift term related to the position of the phase center of the n-th antenna in the set of direction finding antennas.

The fourth step of determining the best configuration consists in retaining the configuration of the set of direction finding antennas having the lowest maximum level of ambiguity among those calculated in the third step, and below a predetermined threshold S _max . This threshold makes it possible to ensure that the maximum level of ambiguities is sufficiently low for the quality of the direction-finding and, if necessary if not, to restart the method according to the invention from the first step in necessarily releasing certain constraints such as, for example, the number of antennas of direction-finding N, that is to say by increasing it.

The preferred values of the threshold S _max are less than or equal to 0.9.

Additional explanations are provided below based on nonlimiting examples illustrated by figures.

Figures 5a and 5b illustrate the phenomenon of goniometry ambiguities by the graphic representation of the correlation function. To facilitate interpretation, the direction of arrival Θ is restricted to the 0 _g deposit, the site 0 _S is assumed to be zero. As previously recommended, the deposit scales are also sine to the deposit. The field of range coverage ranges from -90 to +90 degrees, and the field of interest ranges from -0 _gi = -15 degrees to 6 _gi = 15 degrees.

FIG. 5a corresponds to the correlation function Tcor (0i, 0 ₂ ) = F _Cor (0 _gl , 0 _g2 ) of the configuration of the set of goniometry antennas described previously by FIG. 3. In this configuration, the N direction-finding antennas have the same radiation pattern pointed in the same direction and are regularly spaced at a step ΔΖ, along the y axis (horizontal), and therefore constitute a set of naturally ambiguous antennas for the length of minimum wave A _min . This results in a multitude of lines 51 in addition to the line 50 which, for its part, is not to be considered as a place of ambiguities. Indeed, FIG. 5b corresponds to the correlation function ^ οΓ /? Έ / · (Θι, Θ ₂ ) = FcorRéf ^ _g i, e _g 2) of the reference antenna array, it illustrates its robustness to ambiguities, that is to say the best possible result in terms of rejection of ambiguities. Only the couples (d _gi , 0 _g2 ) belonging to the line 50 passing through the origin, ^- @ 92 'provide a value of F _CorRéf (e _gl , 0 _g2 ) equal to 1, which is absolutely normal.

It will be noted that, on these graphic representations of the correlation functions, the thickness of the lines 50, 51 reflects the achievable precision on the estimate of direction of arrival. The finer the line 50, 51, the more precise the estimate of the deposit. Indeed, the thickness of these straight lines reflects the speed at which the pointing vectors decorrelate as we move away from the arrival directions. The precision of the direction of arrival follows directly from this decorrelation speed, which is itself linked to the geometric dimensions of the set of direction finding antennas.

It will also be noted in FIG. 5a that the spacing 52 between lines 50, 51 is regular and is worth precisely. This is due to the fact that two deposits B _gi and 0 _g2 have similar pointing vectors when the difference of their sine is worth an integer of times This similarity, for this non-zero integer, generates the ambiguities which are normal here given the geometry of the configuration and result in the highest value of the correlation function, i.e. 1.

FIG. 6 presents an exemplary embodiment of a set of direction-finding antennas 70 with diversity of polarization and the possible positions of these antennas 71, 72. As for FIG. 3, in order not to overload the figure, only the possible locations 730 of the phase centers 73 of each of the direction finding antennas 71, 72 have been shown. The materialized configuration is directly inspired by the materialized configuration of the set of monopolarization antennas of FIG. 3 and each antenna 71, 72 is aligned according to a regular mesh. In this example, the set of polarization diversity goniometry antennas 70 comprises twice as many antennas distributed over the same surface to achieve the same precision of direction of arrival as in the configuration shown in FIG. 3. Half antennas 71 has a suitable rectilinear horizontal polarization and the other half of the antennas 72 has a suitable rectilinear vertical polarization.

In general, the antennas 71 are of polarization adapted orthogonal to that of the antennas 72, and these antennas 71, 72 can be arranged in any way to form the set of antennas of direction-finding provided that as many antennas 71 than antennas 72.

According to a particular embodiment, the antennas forming the set of direction-finding antennas can be arranged in a checkerboard pattern by alternating an antenna 71 and an antenna 72. Advantageously, this checkerboard bipolarization architecture allows:

- To standardize the probability of interception of the incident signals on the set of direction finding antennas according to their polarization;

- To allow a joint estimation of the direction of arrival and the polarization of the intercepted signal;

- Optimizing the direction of arrival on site and in deposit.

According to another embodiment, the set of goniometry antennas 70 with diversity of polarization consists of double antennas, called bipolarization and comprising two antennas of orthogonal adapted polarizations whose phase centers are coincident with imperfections. In this case, the number of bipolarization antennas is identical to that of a set of monopolarization antenna 30.

FIG. 7 corresponds to the correlation function / γτοΛθι, θ2) ⁼ Pcor (.dg ₁ , e _g 2 ^> ) for the configuration materialized in FIG. 6. The regular arrangement of the antennas 71, 72 causes ambiguities of maximum level. For areas of coverage and interest identical to Figure 5a, Figure 7 has half the lines, which is normal because the spacing along the y-axis (horizontal) between two successive antennas is reduced in a ratio two.

FIG. 8a gives an example of configuration of a set of direction finding antennas 80 designed according to the invention. This configuration was chosen from a list of ten thousand possible configurations obtained by a succession of random draws. For a direction of arrival direction of interest comprising deposits between -15 and +15 degrees and sites between -10 and +10 degrees, the correlation function F _Cor (Qi'®2) is less than 0.75 . Figure 8b graphically represents the correlation function Fcor (.®i> ®2) = Fcor ^ g!, E _g2 ') at zero site for deposits of interest between -15 and +15 degrees and coverage deposits between -90 and +90 degrees, the value of this function has a value less than 0.7 outside the straight line 50. The comparison of Figures 5a and 8b makes it possible to highlight the significant reduction in the level of ambiguities of the whole direction finding antennas, the precision of direction of arrival being unchanged.

FIG. 9a gives an example of configuration of a set of goniometry antennas 90 with polarization diversity designed according to the invention. This configuration was chosen from a list of a million possible configurations obtained by a succession of random draws. For a direction of arrival direction of interest comprising deposits between -15 and +15 degrees and sites between -10 and +10 degrees, the correlation function F _Cor (Q ₁ , Q ₂ ') is less than 0 , 85. Figure 9b graphically represents the correlation function F _Cor (B ₁ , Q ₂ ') = F _Cor (e _gil 0g2) at zero site for deposits of interest between -15 and +15 degrees and coverage deposits between - 90 and +90 degrees, the value of this function has a value less than 0.5 outside the straight line 50. The comparison of Figures 7 and 9b makes it possible to highlight the significant reduction in the level of ambiguities of the set d goniometry antennas, the precision of direction of arrival being unchanged.

Claims (6)

Method for manufacturing a set of direction finding antennas (70, 80, 90) in two dimensions comprising at least three antennas, characterized in that, comprising a phase of determining the optimal configuration of said set from a list of possible configurations , a configuration being defined by the gain, the pointing direction and the position within said set of each of said antennas, said phase comprises at least: - A step (21) of defining a network of reference antennas, said array covering a surface having a dimension in site and / or in deposit inversely proportional respectively to a level of precision required in site and / or in deposit for the estimation of the directions of arrival of the incident waves, and comprising a plurality of elementary antennas, said elementary antennas being distributed in a regular mesh, the distance separating two contiguous elementary antennas being substantially equal to the half-wavelength associated with the maximum frequency of a range of frequencies of interest, - A step (22) of searching for configurations to be taken into consideration from predetermined constraints in order to establish a list of configurations to be taken into account, - A step (23) of quantifying the maximum level of ambiguity of each of the configurations of said list from a correlation function in order to associate with each of said configurations an evaluation quantity, - A step (24) of searching for the configuration having the lowest evaluation quantity, said configuration being the optimal configuration. Method according to Claim 1, in which the said set of direction finding antennas is intended for measurements of the direction of arrival of incident radio signals not dependent on the polarization of said signals, the evaluation quantity associated with a configuration is equal at the maximum value of a correlation function Pcor (© i, © ₂ ) function of two directions of arrival where © t and 0 ₂ representing two directions of arrival sweeping the area of coverage of direction of arrival of said configuration for one and the direction of arrival direction of interest for the other, and excluding the values for which the correlation function of said array of reference antennas F _CorRéf (© i, © ₂ ) is greater or equal to a predetermined threshold S _Ref , the correlation functions Fcor (®1, © 2) and ^ corffé / ( ⁰ i »®2) expressing themselves respectively from the pointing vector of said configuration and from the poi vector ntage of said reference set. Method according to claim 1, in which said set of antennas is intended for measurements of direction of arrival of incident radio signals depending on the polarization of said signals, the evaluation quantity associated with a configuration is equal to the maximum value eigenvalues of a matrix Γ * (© ι, © ₂ ) · Γ (Θ _{1 (} © ₂ ), function of two directions of arrival where © i and © ₂ representing two directions of arrival sweeping the area of coverage angular of said configuration for one and the angular domain of interest for the other, where: [(© i, r (©!, © ₂ ) = ^ -min) Uvnorm (.®2> 7-min)] Uv normal ’^ -min) OR Γ (Θ _{1 (} © ₂ ) is a 2x2 square matrix; ^ Hnorm ( ⁰ l <^ -min) Uvnormfôl '^ -min) · is a matrix 2 x N; [^ Hnorm (.®2i ^ -min) Uv _n orm (®2> A JV X 2 matrix, - VfinorrM * min) and U _Vnorm (®, X _min ) are two vectors forming an orthonormal base of the plane generated by the two pointing vectors Î / _H (©, Â _min ) and of the set of goniometry antennas at the minimum wavelength, respectively in horizontal rectilinear polarization and in vertical rectilinear polarization, - The sign * corresponds to the transposed and conjugated transformation. 4. Method according to one of the preceding claims, in which the list of configurations to be taken into account corresponds to the complete list of possible configurations. 5. Method according to one of claims 1 to 3 wherein the list of 5 configurations to be taken into account corresponds to a random selection of a predetermined number of configurations from the complete list of possible configurations. 6. Method according to one of the preceding claims in which the reference antenna array antennas are aligned according to a 10 mesh, the positions in the possible configurations of the antennas of the set of direction finding antennas are aligned on said mesh. 7. Method according to one of the preceding claims, in which said array of reference antennas is an array of radiating elements, 15 each antenna of said set of direction finding antennas being produced from a sub-network of said network. 8. A set of direction finding antennas, characterized in that it is produced by the method according to any one of the preceding claims. 1/8 Arrival direction (Θ) 110